Positive active material for lithium secondary battery, precursor of positive active material, electrode for lithium secondary battery and lithium secondary battery

ABSTRACT

Provided is a positive active material for a lithium secondary battery includes a lithium transition metal composite oxide having an α-NaFeO 2 -type crystal structure and represented by the composition formula of Li 1+α Me 1−α O 2  (Me is a transition metal including Co, Ni and Mn and α&gt;0). The positive active material contains Na in an amount of 900 ppm or more and 16000 ppm or less, or K in an amount of 1200 ppm or more and 18000 ppm or less.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based on Japanese Application No. 2012-138419 filedwith the Japan Patent Office on Jun. 20, 2012, Japanese Application No.2012-138638 filed with the Japan Patent Office on Jun. 20, 2012 andJapanese Application No. 2013-051267 filed with the Japan Patent Officeon Mar. 14, 2013, the entire contents of which are hereby incorporatedby reference.

FIELD

The present invention relates to a positive active material for alithium secondary battery, a precursor of the positive active material,an electrode for a lithium secondary battery which contains the positiveactive material, and a lithium secondary battery including theelectrode.

BACKGROUND

Currently, nonaqueous electrolyte secondary batteries represented bylithium ion secondary batteries, particularly lithium secondarybatteries, are widely mounted on portable terminals, and so on. Forthese nonaqueous electrolyte secondary batteries, principally LiCoO₂ isused as a positive active material. However, the discharge capacity ofLiCoO₂ is about 120 to 130 mAh/g.

As a material of a positive active material for a lithium secondarybattery, a solid solution of LiCoO₂ and other compounds are known.Li[Co_(1-2x)Ni_(x)Mn_(x)]O₂ (0<x≦½), a solid solution having anα-NaFeO₂-type crystal structure and formed of three components: LiCoO₂,LiNiO₂ and LiMnO₂, was published in 2001. LiNi_(1/2)Mn_(1/2)O₂ orLiCo_(1/3)Ni_(1/3)Mn_(1/3)O₂ that is one example of the aforementionedsolid solution has a discharge capacity of 150 to 180 mAh/g, and is alsoexcellent in terms of charge-discharge cycle performance.

In contrast with so called a “LiMeO₂-type” active material as describedabove, so called a “lithium-excess-type” active material is known inwhich the composition ratio Li/Me of lithium (Li) to the ratio of atransition metal (Me) is greater than 1, with Li/Me being, for example,1.25 to 1.6 (see, for example, U.S. Pat. Nos. 6,677,082, 7,135,252,JP-A-10-106543 and JP-A-2010-86690). This material can be denoted asLi_(1+α)Me_(1−α)O₂ (α>0). Here, β=(1+α)/(1−α) when the composition ratioLi/Me of lithium (Li) to the ratio of a transition metal (Me) is β, andtherefore, for example, α=0.2 when Li/Me is 1.5.

U.S. Pat. Nos. 6,677,082 and 7,135,252 describe an active material for alithium secondary battery, which has a general formula ofxLiMO₂.(1−x)Li₂M′O₃(0<x<1). The documents also describe that M is atleast one selected from Mn, Co and Ni and that M′ is Mn. The documentsshow that the active material enriched in Li has a stabilized crystalstructure, and a lithium secondary battery having a high dischargecapacity is obtained by using this active material.

JP-A-10-106543 describes “a lithium battery comprising a positive activematerial which is formed of a composite oxide having a compositionrepresented by Li_(X)Me_(Y)A_((1-Y))O_((1+X)) (where 1.3≦X≦2.5,0.5≦Y≦0.999) where Me is at least one transition metal selected from 7Aand 8A groups of the periodic table, Mt is a transition metal differentfrom Me, and A is at least one element selected from the groupconsisting of Mt, Na, K, Rb, Cs, Al, Ga, In, Tl, B, Mg, Ca, Sr, Ba andPb, and having a hexagonal crystal structure” (claim 1). The documentshows that the positive active material enriched in Li has a stabilizedcrystal structure, and a lithium battery having a high energy density isobtained by using this positive active material. The document also showsas Example a positive active material wherein x is 1.3, Me is Mn and Ais Co.

JP-A-2010-86690 describes the invention of “an active material for alithium secondary battery comprising a solid solution of a lithiumtransition metal composite oxide having an α-NaFeO₂-type crystalstructure, wherein the composition ratio of Li, Co, Ni and Mn containedin the solid solution satisfiesLi_(1+1/3x)Co_(1-x-y)Ni_(y/2)Mn_(2x/3+y/2) (x+y≦1, 0≦y, 1−x−y=z), (x, y,z) is represented by a value present on the line of or within a heptagonABCDEFG having point A (0.45, 0.55, 0), point B (0.63, 0.37, 0), point C(0.7, 0.25, 0.05), point D (0.67, 0.18, 0.15), point E (0.75, 0, 0.25),point F (0.55, 0, 0.45) and point G (0.45, 0.2, 0.35) as apexes, in aLi[Li_(1/3)Mn_(2/3)]O₂(x)-LiNi_(1/2)Mn_(1/2)O₂(y)-LiCoO₂(z)-systemtriangular phase diagram, and the intensity ratio of the diffractionpeak of the (003) line and the (104) line in X-ray diffractionmeasurement is I₍₀₀₃₎/I₍₁₀₄₎≧1.56 before charge-discharge, andI₍₀₀₃₎/I₍₁₀₄₎>1 at the end of discharge” (claim 1). The document showsthat by using the active material enriched in Li, a lithium secondarybattery, which has a high discharge capacity, and particularly has ahigh discharge capacity in a potential range of 4.3 V or less, isobtained.

On the other hand, it is also known that a positive active material fora lithium secondary battery, which contains a lithium transition metalcomposite oxide formed of Li and transition metal elements (Co, Ni, Mnand the like) contains an alkali component (see JP-A-2011-124086,JP-A-2009-140787 and International Publication No. WO 2012/039413).

JP-A-2011-124086 describes the invention of “a positive active materialfor a lithium secondary battery which comprises a lithium compositeoxide represented by the following formula (I):Li_((x))Ni_((1-a-b))Co_((a))Mn_((b))O₂ (1) (where x is 0.98≦x≦1.20, a is0<a≦0.5, and b is 0<b≦0.5), wherein the amount of residual alkalipresent on the surface part of a primary particle is 4000 ppm or less,and the amount of sulfate radicals present on the surface part of theprimary particle is 500 to 11000 ppm” (claim 1), and “a positive activematerial for a lithium secondary battery which is obtained by a firstsintering step of sintering at 950° C. or lower a sintering raw materialmixture containing a lithium compound, a nickel compound, a cobaltcompound and a manganese compound to obtain a lithium composite oxiderepresented by the following formula (I):Li_((x))Ni_((1-a-b))Co_((a))Mn_((b))O₂ (1) (where x is 0.98≦x≦1.20, a is0<a≦0.5, and b is 0<b≦0.5); an aqueous sulfate solution treatment stepcomprising washing and contacting with an aqueous sulfate solution thelithium composite oxide obtained in the first sintering step andrepresented by the general formula (1), so that an aqueous sulfatesolution treatment product is obtained; and a second sintering stepcomprising sintering the aqueous sulfate solution treatment product at400 to 800° C. to obtain a positive active material for a lithiumsecondary battery” (claim 4). An object of the invention is to “providea lithium nickel cobalt manganese-based composite oxide which has areduced amount of residual alkali present on the surface part of aprimary particle and is excellent in cycle performance” (paragraph[0011]).

JP-A-2011-124086 describes that “for the amount of residual alkalipresent on the surface part of a primary particle of a positive activematerial, 5 g of a sample and 100 g of ultrapure water were weighed andtaken in a beaker, and dispersed at 25° C. for 5 minutes using amagnetic stirrer; then, the dispersion was filtered, 30 ml of thefiltrate was titrated with 0.1 N-HCl by an automatic titrator (model:COMTITE-2500), and the amount of residual alkali present in the sample(value obtained by measuring the amount of lithium and calculating itinto the amount of lithium carbonate) was calculated.” (paragraph[0103]).

JP-A-2009-140787 describes the invention of “a positive active materialused in a nonaqueous electrolyte secondary battery, wherein the positiveactive material is a lithium-nickel-cobalt-manganese composite oxide,and the lithium-nickel-cobalt-manganese composite oxide containstungsten and niobium” (claim 1) and “the positive active materialaccording to any one of claims 1 to 3, wherein the content of thewater-soluble alkali contained in the lithium-nickel-cobalt-manganesecomposite oxide is 0.2 wt % or less” (claim 4). An object of theinvention is to “provide a positive active material which has anexcellent power characteristic and generates a reduced amount of gas,and a battery using the positive active material” (paragraph [0009]).

JP-A-2009-140787 also describes that “50 ml of pure water is added to 10g of a positive active material, and the resulting mixture is stirredfor an hour, and then filtered; the filtrate is diluted to anappropriate concentration, followed by adding phenolphthalein as anindicator, and carrying out titration with a H₂SO₄ solution; the weightratio of lithium hydroxide to the positive active material from theresult of titration on the presumption that the alkali neutralized withthe H₂SO₄ solution is all lithium hydroxide; and this value is definedas a content of water-soluble alkali” (paragraph [0056]).

International Publication No. WO 2012/039413 describes the invention of“an active material for a lithium secondary battery, comprising a solidsolution of a sodium-containing lithium transition metal composite oxidehaving an α-NaFeO₂-type crystal structure, wherein the chemicalcomposition formula of the solid solution satisfiesLi_(1+x-y)Na_(y)Co_(a)Ni_(b)Mn_(c)O_(2+d) (0<y≦0.1, 0.4≦c≦0.7,x+a+b+c=1, 0.1≦x≦0.25, −0.2≦d≦0.2), the active material has an X-raydiffraction pattern attributable to a hexagonal crystal (space groupP3₁12), and in the Miller index hkl, the half width of the diffractionpeak of the (003) is 0.30° or less and the half width of the diffractionpeak of the (114) line is 0.50° or less” (claim 1). The document showsthat according to the invention, “an active material for a lithiumsecondary battery, which has a high initial efficiency and a highdischarge capacity, and particularly has a high discharge capacity at alow temperature, can be provided” (paragraph [0038]). Also, it is shownas Example that the content of Na (value of y described above) is set at0.01 to 0.1 mol (see Table 1) by a method using a coprecipitationhydroxide precursor.

The discharge capacity of so called a “lithium-excess-type” activematerial as described above is generally higher than that of so called a“LiMeO₂-type” active material. In recent years, however, an activematerial with a further high discharge capacity has been required forlithium secondary batteries that are used in the field of automobilessuch as electric cars, hybrid cars and plug-in hybrid cars.

SUMMARY

The following presents a simplified summary of the invention disclosedherein in order to provide a basic understanding of some aspects of theinvention. This summary is not an extensive overview of the invention.It is intended to neither identify key or critical elements of theinvention nor delineate the scope of the invention. Its sole purpose isto present some concepts of the invention in a simplified form as aprelude to the more detailed description that is presented later.

The present invention has been devised in view of the above-mentionedproblem, and one object thereof is to provide a positive active materialfor a lithium secondary battery, which has a high discharge capacity,and particularly has a high discharge capacity even when such a chargemethod that the maximum potential of the positive electrode duringcharge is lower than 4.5 V (vs. Li/Li⁺), for example 4.3 V (vs. Li/Li⁺)or less is employed, and a lithium secondary battery using the positiveactive material.

An aspect of the present invention includes a positive active materialfor a lithium secondary battery, which includes a lithium transitionmetal composite oxide having an α-NaFeO₂-type crystal structure andrepresented by the composition formula of Li_(1+α)Me_(1−α)O₂ (Me is atransition metal including Co, Ni and Mn and α>0). The positive activematerial contains Na in an amount of 900 ppm or more and 16000 ppm orless, or K in an amount of 1200 ppm or more and 18000 ppm or less.

DESCRIPTION OF EMBODIMENTS

A positive active material for a lithium secondary battery according toan aspect of the present invention includes a lithium transition metalcomposite oxide having an α-NaFeO₂-type crystal structure andrepresented by the composition formula of Li_(1+α)Me_(1−α)O₂(Me is atransition metal including Co, Ni and Mn and α>0). The positive activematerial contains Na in an amount of 900 ppm or more and 16000 ppm orless, or K in an amount of 1200 ppm or more and 18000 ppm or less.

Another aspect of this positive active material for a lithium secondarybattery has a 50% particle size (D50) of 8 to 10 μm in particle sizedistribution measurement.

In another aspect of this positive active material for a lithiumsecondary battery has a molar ratio of Li to Me, which is represented by(1+α)/(1−α), is 1.25 to 1.45.

A carbonate precursor of a positive active material for a lithiumsecondary battery according to the present invention contains Na in anamount of 900 ppm or more and 2100 ppm or less and has a 50% particlesize (D50) of 8 to 10 μm in particle size distribution measurement. Thecarbonate precursor is represented by MeCO₃ (Me is a transition metalincluding Co, Ni and Mn).

A method for production of the positive active material for a lithiumsecondary battery according to the present invention includes adding asodium compound together with a lithium compound to a carbonateprecursor containing Na and represented by MeCO₃ (Me is a transitionmetal including Co, Ni and Mn) in a sintering step. The positive activematerial contains Na in an amount of 3000 ppm or more and 16000 ppm orless.

A method for production of the positive active material for a lithiumsecondary battery according to the present invention includes adding apotassium compound together with a lithium compound to a carbonateprecursor containing K and represented by MeCO₃ (Me is a transitionmetal including Co, Ni and Mn) in a sintering step. The positive activematerial contains K in an amount of 1200 ppm or more and 18000 ppm orless.

An electrode for a lithium secondary battery according to the presentinvention includes the positive active material for a lithium secondarybattery described above.

Additionally, a lithium secondary battery according to the presentinvention includes the electrode for a lithium secondary batterydescribed above.

According to the aspects of the present invention, a lithium secondarybattery, which includes a positive active material containing a novellithium transition metal composite oxide and which has a high dischargecapacity, can be provided.

The composition of a lithium transition metal composite oxide containedin an active material for a lithium secondary battery according to thepresent invention can be denoted as Li_(1+α)Me_(1−α)O₂ (α>0) whichcontains a transition metal element Me including Co, Ni and Mn as wellas Li. The lithium transition metal composite oxide is so called a“lithium-excess type” which has a high discharge capacity.

The ratio of elements such as Co, Ni and Mn which form a transitionmetal element that forms the lithium transition metal composite oxidecan be arbitrarily selected according to required characteristics.

In the present invention, the molar ratio of Li to the transition metalelement Me (Li/Me), which is represented by (1+α)/(1−α) in thecomposition formula of Li_(1+α)Me_(1−α)O₂, is preferably 1.2 to 1.6because a lithium secondary battery having a high discharge capacity canbe obtained. Above all, a composition in which the ratio of Li/Me is1.25 to 1.45 is more preferably selected to obtain a lithium secondarybattery which has a particularly high discharge capacity and isexcellent in high rate discharge characteristics.

The molar ratio of Co to the transition metal element Me (Co/Me) ispreferably 0.02 to 0.23, more preferably 0.04 to 0.21, most preferably0.06 to 0.17, to obtain a lithium secondary battery which has a highdischarge capacity and is excellent in initial charge-dischargeefficiency.

The molar ratio of Mn to the transition metal element Me (Mn/Me) ispreferably 0.63 to 0.72, more preferably 0.65 to 0.71, to obtain alithium secondary battery which has a high discharge capacity and isexcellent in initial charge-discharge efficiency.

In the present invention, the lithium transition metal composite oxiderepresented by the composition formula of Li_(1+α)Me_(1−α)O₂ (Me is atransition metal including Co, Ni and Mn and α>0) contains Na in anamount of 900 ppm or more and 16000 ppm or less. Improvement of thedischarge capacity is not sufficient if the content of Na is less than900 ppm, while the discharge capacity starts to decrease, pastestability is deteriorated, and processability in preparation of theelectrode is deteriorated if the content of Na is more than 16000 ppm.Therefore, for improving the discharge capacity, the content of Na isset to be 900 ppm or more and 16000 ppm or less. The content of Na ispreferably 1000 ppm or more and 14000 ppm or less, more preferably 1500ppm or more and 12000 ppm or less, especially preferably 3000 ppm ormore and 10000 ppm or less.

For adjusting the content of Na to the range described above, a methodin which in a step of preparing a hydroxide precursor as describedlater, a sodium compound such as sodium hydroxide is used as aneutralizer, so that Na remains in a washing step, and/or a method inwhich in a subsequent sintering step, a sodium compound such as sodiumcarbonate is added can be employed.

In the present invention, the carbonate precursor of the positive activematerial for a lithium secondary battery is represented by MeCO₃ (Me isa transition metal including Co, Ni and Mn), and contains Na in anamount of 900 ppm or more and 2100 ppm or less.

Residual Na in the neutralization/washing step during preparation of theprecursor may act as a primary particle growth suppressing agent in astep of sintering so called a “lithium-excess-type” lithium transitionmetal composite oxide. The electrode characteristic of a lithiumsecondary battery including the lithium transition metal composite oxideas a positive active material may be improved.

For adjusting the content of Na to a range of 3000 ppm or more and 16000ppm or less, a method is employed in which Na is made to remain in awashing step as described above, and a sodium compound such as sodiumcarbonate is added in a subsequent sintering step.

In another aspect of the present invention, the lithium transition metalcomposite oxide represented by the composition formula ofLi_(1+α)Me_(1−α)O₂ (Me is a transition metal including Co, Ni and Mn andα>0) contains K in an amount of 1200 ppm or more and 18000 ppm or less.Improvement of the discharge capacity is not sufficient if the contentof K is less than 1200 ppm, while the discharge capacity starts todecrease if the content of K is more than 18000 ppm. Therefore, forimproving the discharge capacity, the content of K is set to be 1200 ppmor more and 18000 ppm or less. The content of K is preferably 1500 ppmor more and 15000 ppm or less, more preferably 2000 ppm or more and15000 ppm or less, especially preferably 4000 ppm or more and 10000 ppmor less.

For adjusting the content of K to the range described above, a potassiumcompound such as potassium carbonate is used as a neutralizer in a stepof preparing a carbonate precursor as described later, so that K remainsin a washing step, and a potassium compound such as potassium carbonateis added in a subsequent sintering step. Since with only potassiumcarbonate that is used as a neutralizer, the content of K does not reach1200 ppm or more when washing is performed, it is preferred to addpotassium carbonate in the sintering step.

The lithium transition metal composite oxide of the present invention isrepresented by the general formula described above, is a composite oxideessentially composed of Li, Co, Ni and Mn, and contains a small amountof Na or K, but inclusion of a small amount of other metals, such asalkali metals other than Na or K, alkali earth metals such as Mg and Caand transition metals represented by 3d transition metals such as Fe andZn within the bounds of not impairing the effect of the presentinvention, is not excluded.

The lithium transition metal composite oxide according to the presentinvention has an α-NaFeO₂ structure. The lithium transition metalcomposite oxide after synthesis (before charge-discharge is performed)is attributed to the space group P3₁12 or R3-m. Among them, in thoseattributed to the space group P3₁12, a superlattice peak (peak found ina (Li[Li_(1/3)Mn_(2/3)]O₂-type monoclinic crystal) is observed at around2θ=21° on an X-ray diffraction pattern using a CuKα bulb. However, whencharge is carried out at least once, so that Li in the crystal isdeintercalated, the symmetry of the crystal is changed, and consequentlythe superlattice peak disappears, and the lithium transition metalcomposite oxide is attributed to the space group R3-m. Here, P3₁12 is acrystal structure model in which atom positions at 3a, 3b and 6c sitesin R3-m are subdivided, and the P3₁12 model is employed when there isorderliness in atom arrangement in R3-m. Properly speaking, “R3-m”should be written with a bar “-” added above “3” of “R3 m”.

The lithium transition metal composite oxide according to the presentinvention is attributed to the space group P3₁12 or R3-m of thehexagonal crystal, and preferably the half width of the diffraction peakat 2θ=18.6°±1° is 0.20° to 0.27° or/and the half width of thediffraction peak at 2θ=44.1°±1° is 0.26° to 0.39° on an X-raydiffraction pattern using a CuKα bulb. In this way, the dischargecapacity of the positive active material can be increased. Thediffraction peak at 2θ=18.6°±1° is indexed to the (003) line in themirror index hkl for space groups P3₁12 and R3-m, and the diffractionpeak at 2θ=44.1°±1° is indexed to the (114) line for the space groupP3₁12 and to the (104) line for the space group R3-m, respectively.

In another aspect of the present invention, the positive active materialfor a lithium secondary battery and the carbonate precursor thereof havea 50% particle size (D50) of 8 to 10 μm or less in particle sizedistribution measurement. When the lithium transition metal compositeoxide is prepared from a hydroxide precursor, excellent performance isnot achieved unless the particle size is controlled to be smaller. Bypreparing the lithium transition metal composite oxide from a carbonateprecursor, an active material having a discharge capacity (0.1 C capa)of 200 mAh/g or more is obtained even when the 50% particle size (D50)in particle size distribution measurement is 8 to 10 μm or less.

An active material prepared by way of a carbonate precursor has a peakdifferential pore volume of 0.85 mm³/(g·nm) or more in a pore region of30 to 50 nm, whereas an active material prepared by way of a hydroxideprecursor has a peak differential pore volume of only about 0.50mm³/(g·nm) in a pore region of 30 to 50 nm, and the differential peak isin a pore region of about 60 nm.

In the lithium transition metal composite oxide according to anotheraspect of the present invention, the pore size, at which thedifferential pore volume determined by a BJH method from an adsorptionisotherm obtained using a nitrogen gas adsorption method shows a maximumvalue, is in a range of 30 to 40 nm, and the peak differential porevolume is 0.85 mm³/(g·nm) or more. Since the peak differential porevolume is 0.85 mm³/(g·nm) or more, a lithium secondary battery excellentin initial efficiency can be obtained. When the peak differential porevolume is 1.76 mm³/(g·nm) or less, a lithium secondary battery, which isnot only excellent in initial efficiency but also particularly excellentin discharge capacity, can be obtained, and therefore the peakdifferential pore volume is preferably 0.85 to 1.76 mm³/(g·nm).

Next, a method for producing the active material for a lithium secondarybattery according to the present invention will be described.

The active material for a lithium secondary battery according to thepresent invention can be obtained essentially by preparing a rawmaterial containing metal elements (Li, Mn, Co and Ni), which form theactive material, in accordance with a desired composition of the activematerial (oxide), and sintering the prepared raw material. For theamount of the Li raw material, however, it is preferable to incorporatethe Li raw material in an excessive amount by about 1 to 5% inconsideration of elimination of a part thereof during sintering.

For preparing an oxide having a desired composition, so called a “solidstate method” in which salts of Li, Co, Ni and Mn are mixed andsintered, and so called a “coprecipitation method” in which acoprecipitation precursor with Co, Ni and Mn existing in one particle isprepared beforehand, and a Li salt is mixed thereto, and the mixture issintered are known. In the synthesis process of the “solid statemethod”, particularly Mn is hard to be uniformly solid soluted with Coand Ni, and therefore it is difficult to obtain a sample in which theelements are uniformly distributed in one particle. So far, in documentsand so on, many attempts have been made to solve Mn with a part of Ni orCo (LiNi_(1-x)Mn_(x)O₂, etc.) by the solid state method, but byselecting the “coprecipitation method”, a uniform phase is more easilyobtained at an element level. Thus, in Examples described later, the“coprecipitation method” is employed.

When a coprecipitation precursor is prepared, Mn is most easily oxidizedamong Co, Ni and Mn, so that it is not easy to prepare a coprecipitationprecursor in which Co, Ni and Mn are homogeneously distributed in adivalent state, and therefore homogeneous mixing of Co, Ni and Mn at anelement level tends to be insufficient. Particularly in the compositionrange in the present invention, the ratio of Mn is high as compared tothe ratios of Co and Ni, and therefore it is particularly important toremove dissolved oxygen in an aqueous solution to prevent Mn fromoxidation. Examples of the method for removing dissolved oxygen includea method in which a gas containing no oxygen is bubbled. The gascontaining no oxygen is not limited, but a nitrogen gas, an argon gas,carbon dioxide (CO₂) or the like can be used. Particularly, when acoprecipitation carbonate precursor is prepared as in Example describedlater, employment of carbon dioxide as a gas containing no oxygen ispreferable because an environment is provided in which the carbonate ismore easily generated.

pH in the step of producing a precursor by coprecipitating in a solutiona compound containing Co, Ni and Mn is not limited, but can be set at7.5 to 11 when the coprecipitation precursor is prepared as acoprecipitation carbonate precursor. It is preferable to control pH forincreasing the tap density. By setting pH at 9.4 or less, it can beensured that the tap density is 1.25 g/cm³ or more, so that high ratedischarge performance can be improved. Further, by setting pH at 8.0 orless, the particle growth rate can be accelerated, so that the stirringduration after completion of dropwise addition of a raw material aqueoussolution can be reduced.

The coprecipitation precursor core is preferably a compound with Mn, Niand Co mixed homogeneously. In the present invention, thecoprecipitation precursor is preferably a carbonate for obtaining anactive material for a lithium secondary battery, which has a highdischarge capacity. A precursor having a higher bulk density can also beprepared by using a crystallization reaction using a complexing agent.At this time, by carrying out mixing/sintering with a Li source, anactive material having a high density, so that the energy density perelectrode area can be increased.

Examples of the raw material of the coprecipitation precursor mayinclude manganese oxide, manganese carbonate, manganese sulfate,manganese nitrate and manganese acetate for the Mn compound, nickelhydroxide, nickel carbonate, nickel sulfate, nickel nitrate and nickelacetate for the Ni compound, and cobalt sulfate, cobalt nitrate andcobalt acetate for the Co compound.

In the present invention, a reaction crystallization method forobtaining a coprecipitation carbonate precursor by adding dropwise a rawmaterial aqueous solution of the coprecipitation precursor into areaction tank kept alkaline is employed. For producing a coprecipitationcarbonate precursor containing Na, a sodium compound such as sodiumcarbonate is used as a neutralizer, but it is preferred to use sodiumcarbonate or a mixture of sodium carbonate and lithium carbonate. Na/Li,which is a molar ratio of sodium carbonate to lithium carbonate, ispreferably 0.85/1.15 [M] or more for ensuring that Na remains in anamount of 900 ppm or more as shown in Example described later. Bysetting Na/Li at 0.85/1.15 [M] or more, the possibility can be reducedthat Na is excessively removed in a subsequent washing step, so that thecontent of Na is less than 900 ppm.

For producing a coprecipitation carbonate precursor containing K, apotassium compound such as potassium carbonate is used as a neutralizer.The possibility that K is excessively removed in a subsequent washingstep can be reduced by using potassium carbonate rather than a mixtureof potassium carbonate and lithium carbonate as shown in Exampledescribed later.

The rate of dropwise addition of the raw material aqueous solutionsignificantly influences homogeneity of the element distribution withinone particle of the coprecipitation precursor generated. Particularly,Mn is hard to form a homogeneous element distribution with Co and Ni,and therefore requires care. For the preferred dropwise addition rate,it depends on the size of the reaction tank, stirring conditions, pH,the reaction temperature and so on, but is preferably 30 ml/min or less.For increasing the discharge capacity, the dropwise addition rate ismore preferably 10 ml/min or less, most preferably 5 ml/min or less.

When a complexing agent is present in the reaction tank, and certainconvection conditions are applied, rotation and revolution, in astirring tank, of particles are promoted by further continuing stirringafter completion of dropwise addition of the raw material aqueoussolution, and in this process, particles are grown stepwise into aconcentric circular sphere while colliding with one another. That is,coprecipitation precursor is formed through reactions in two stages,i.e. a metal complex formation reaction when the raw material aqueoussolution is added dropwise into the reaction tank and a precipitateformation reaction that occurs during retention of the metal complex inthe reaction tank. Therefore, by appropriately selecting a time duringwhich stirring is further continued after completion of dropwiseaddition of the raw material aqueous solution, a coprecipitationprecursor having a desired particle size can be obtained.

For the preferred time during which stirring is continued aftercompletion of dropwise addition of the raw material aqueous solution, itdepends on the size of the reaction tank, stirring conditions, pH, thereaction temperature and so on, but is, for example, preferably 0.5 h ormore, more preferably 1 h or more for growing particles as uniformspherical particles. For reducing the possibility that the particle sizeis so large that the power performance of the battery in the low-SOCregion is not sufficient, the time is preferably 15 h or less, morepreferably 10 h or less, most preferably 5 h or less.

The preferred stirring duration time for ensuring that D50, i.e. aparticle size is 8 to 10 μm, at which the cumulative volume in theparticle size distribution of secondary particles of the carbonateprecursor and the lithium transition metal composite oxide is 50%,varies depending on controlled pH. For example, the stirring durationtime is preferably 5 to 7 h when pH is controlled to 8.3 to 8.9, and thestirring duration time is preferably 3 to 5 h when pH is controlled to7.5 to 8.0.

When particles of the carbonate precursor are prepared using as aneutralizer a sodium compound such as sodium carbonate, sodium ionsattached on particles are washed off in a subsequent washing step, andin the present invention, it is necessary to wash off sodium ions undersuch conditions that Na remains in an amount of 900 ppm or more. Whenparticles of the carbonate precursor are prepared using as a neutralizera potassium compound such as potassium carbonate, potassium ionsattached on particles are washed off in a subsequent washing step, andin the present invention, it is preferred to wash off potassium ionsunder such conditions that K remains in an amount of 1000 ppm or more.For example, such conditions that the number of washings with 200 ml ofion-exchange water is 5 can be employed when the prepared carbonateprecursor is extracted by suction filtration.

Preferably the carbonate precursor is dried under normal pressure in anair atmosphere at a temperature of 80° C. to lower than 100° C. A largeramount of moisture can be removed in a short time when the carbonateprecursor is dried at 100° C. or higher, but an active material showingmore excellent electrode characteristics can be formed when thecarbonate precursor is dried at 80° C. for a long time. Although thereason for this is not necessarily evident, the carbonate precursor is aporous material having a specific surface area of 50 to 100 m²/g, andtherefore has a structure in which moisture is easily adsorbed. Thus,the inventor presumes as follows: When the carbonate precursor is driedat a low temperature to ensure that measurable adsorbed water remains ina pore in the state of the precursor. Molten Li can enter the pore insuch a manner as to replace adsorbed water that is removed from the porein a sintering step of mixing the carbonate precursor with a Li salt andsintering the mixture. Consequently an active material having a moreuniform composition is obtained as compared to the case where thecarbonate precursor is dried at 100° C. Since a carbonate precursorobtained by performing drying at 100° C. shows is deep brown, while acarbonate precursor obtained by performing drying at 80° C. isfresh-colored, a distinction can be made by the color of the precursor.

Thus, for quantitatively evaluating the above-described differencebetween the precursors, the color phase of each precursor was measuredand compared with JPMA Standard Paint Colors (Edition F, 2011) beingcompliant with JIS Z 8721 and issued by Japan Paint ManufacturersAssociation. For measurement of the color phase, Color Leader CR10manufactured by KONICA MINOLTA, INC was used. According to thismeasurement method, the value of dL* that represents a brightness islarger when the sample is more whitish, and is smaller when the sampleis more blackish. The value of da* that represents a color phase islarger when the sample is more reddish, and is smaller when the sampleis more greenish (less reddish). The value of db* that represents acolor phase is larger when the sample is more yellowish, and is smallerwhen the sample is more bluish (less yellowish).

It has become apparent that the color phase of a product by drying at100° C. (Comparative Example) is within a range in which the standardcolor F05-40D is attained in a red direction as compared to the standardcolor F05-20B, and is within a range in which the standard color FN-25is attained in a white direction as compared to the standard colorFN-10. It has been found that above all, a color difference between theabove-mentioned color phase and a color phase exhibited by the standardcolor F05-20B is smallest.

It has become apparent that the color phase of a product by drying at80° C. (Example) is within a range in which the standard color F19-70Fis attained in a white direction as compared to the standard colorF19-50F, and is within a range in which the standard color F09-60H isattained in a black direction as compared to the standard color F09-80D.It has been found that above all, a color difference between theabove-mentioned color phase and a color phase exhibited by the standardcolor F19-50F is smallest.

From the above findings, it can be said that preferably the color phaseof the carbonate precursor is in the + direction in all of dL, da and dbas compared to the standard color F05-20B, and more preferably dL is +5or more, da is +2 or more, and db is +5 or more.

The active material for a lithium secondary battery according to thepresent invention can be suitably prepared by mixing the carbonateprecursor and a Li compound, followed by heat-treating the mixture. Byusing, as the Li compound, lithium hydroxide, lithium carbonate, lithiumnitrate, lithium acetate or the like, the active material can besuitably produced. For the amount of the Li compound, however, it ispreferable to incorporate the Li compound in an excessive amount byabout 1 to 5% in consideration of elimination of a part thereof duringsintering.

In the present invention, a Na compound is preferably mixed with thecarbonate precursor containing Na, together with a Li compound, in thesintering step for ensuring that the content of Na in the lithiumtransition metal composite oxide is 3000 ppm or more. The Na compound ispreferably sodium carbonate. The content of Na in the carbonateprecursor is about 900 to 2100 ppm, but the content of Na can beincreased to 3000 ppm or more by mixing a Na compound.

In the present invention, a K compound is mixed with the carbonateprecursor containing the K, together with a Li compound, in thesintering step for ensuring that the content of K in the lithiumtransition metal composite oxide is 1200 ppm or more. The K compound ispreferably potassium carbonate. The content of K in the carbonateprecursor is 1000 ppm or less, but the content of K can be increased to1200 ppm or more by mixing a K compound.

The sintering temperature influences the reversible capacity of theactive material.

If the sintering temperature is too high, there is such a tendency thatthe obtained active material is collapsed with an oxygen releasereaction, and a phase defined as a Li[Li_(1/3)Mn_(2/3)]O₂ type of amonoclinic crystal, in addition to a hexagonal crystal as a main phasetends to be observed as a separate phase rather than a solid solutionphase. Inclusion of this separate phase in a too large amount is notpreferable because the reversible capacity of the active material isreduced. In this material, impurity peaks are observed at around 35° andat around 45° on the X-ray diffraction pattern. Therefore, the sinteringtemperature is preferably lower than a temperature at which the oxygenrelease reaction of the active material is influential. Therefore, it isimportant to ensure that the sintering temperature is lower than atemperature at which the oxygen release reaction of the active materialis influential. The oxygen release temperature of the active material isgenerally 1000° C. or higher in the composition range according to thepresent invention, but since the oxygen release temperature slightlyvaries depending on the composition of the active material, it ispreferable to check the oxygen release temperature of the activematerial beforehand. Particularly, it should be noted that the oxygenrelease temperature has been found to shift toward the low temperatureside as the amount of Co contained in the active material increases. Asa method for checking the oxygen release temperature of the activematerial, a mixture of a coprecipitation precursor with Li compound maybe subjected to thermogravimetric analysis (DTA-TG measurement) forsimulating a sintering reaction process, but in this method, platinumused in a sample chamber of a measuring instrument may be corroded by avolatilized Li component to damage the instrument, and therefore acomposition that is crystallized on some level beforehand by employing asintering temperature of about 500° C. should be subjected tothermogravimetric analysis.

On the other hand, if the sintering temperature is too low, there issuch a tendency that crystallization does not sufficiently proceed, andthe electrode characteristic is degraded. In the present invention, thesintering temperature is preferably at least 700° C. By ensuringsufficient crystallization, the resistance of a crystal grain boundarycan be reduced to facilitate smooth transportation of lithium ions.

Furthermore, the inventors precisely analyzed the half width of theactive material of the present invention to find that a strain remainedin a lattice in the active material synthesized at a temperature of upto 750° C., and the strain could be mostly removed by synthesizing theactive material at a higher temperature. The size of the crystallite wasincreased proportionally as the synthesis temperature was elevated.Therefore, in the composition of the active material of the presentinvention, a good discharge capacity was also obtained by aiming forparticles in which the strain of the lattice is little present in alattice, and the crystallite size is sufficiently grown. Specifically,it has been found that it is preferable to employ such a synthesistemperature (sintering temperature) that the amount of strain having aneffect on the lattice constant is 2% or less, and the crystallite sizeis grown to 50 nm or more. When these particles are molded as anelectrode and charge-discharge is performed, a change occurs due toexpansion and contraction, but it is preferable for effect of presentinvention that the crystallite size to be kept at 30 nm or more even ina charge-discharge process. That is, an active material having a highreversible capacity can be obtained only by selecting the sinteringtemperature so as to be as close as possible to the above-describedoxygen release temperature of the active material.

As described above, the preferred sintering temperature varies dependingon the oxygen release temperature of the active material, and it istherefore difficult to uniformly set a preferred range of the sinteringtemperature, but for making the discharge capacity sufficiently highwhen the molar ratio of Li/Me is 1.2 to 1.6, the sintering temperatureis preferably 700 to 950° C., and more preferably around 700 to 900° C.particularly when Li/Me is 1.25 to 1.45.

The nonaqueous electrolyte used in the lithium secondary batteryaccording to the present invention is not limited, and those that aregenerally proposed to be used in lithium batteries and the like can beused. Examples of the nonaqueous solvent used in the nonaqueouselectrolyte may include, but are not limited to, cyclic carbonates suchas propylene carbonate, ethylene carbonate, butyrene carbonate,chloroethylene carbonate and vinylene carbonate; cyclic esters such asγ-butyrolactone and γ-valerolactone; chain carbonates such as dimethylcarbonate, diethyl carbonate and ethylmethyl carbonate; chain esterssuch as methyl formate, methyl acetate and methyl butyrate;tetrahydrofuran or derivatives thereof ethers such as 1,3-dioxane,1,4-dioxane, 1,2-dimethoxyethane, 1,4-dibutoxyethane and methyl diglyme;nitriles such as acetonitrile, benzonitrile; dioxolane or derivativesthereof; and ethylene sulfide, sulfolane, sultone or derivatives thereofalone or mixtures of two or more thereof.

Examples of the electrolyte salt used in the nonaqueous electrolyteinclude inorganic ion salts having one of lithium (Li), sodium (Na) andpotassium (K), such as LiClO₄, LiBF₄, LiAsF₆, LiPF₆, LiSCN, LiBr, LiI,Li₂SO₄, Li₂B₁₀Cl₁₀, NaClO₄, NaI, NaSCN, NaBr, KClO₄, KSCN, and organicion salts such as LiCF₃SO₃, LiN(CF₃SO₂)₂, LiN(C₂F₅SO₂)₂,LiN(CF₃SO₂)(C₄F₉SO₂), LiC(CF₃SO₂)₃, LiC(C₂F₅SO₂)₃, (CH₃)₄NBF₄,(CH₃)₄NBr, (C₂H₅)₄NClO₄, (C₂H₅)₄NI, (C₃H₇)₄NBr, (n-C₃H₉)₄NClO₄,(n-C₄H₉)₄NI, (C₂H₅)₄N-maleate, (C₂H₅)₄N-benzoate, (C₂H₅)₄N-phtalate,lithium stearylsulfonate, lithium octylsulfonate and lithiumdodecylbenzenesulfonate, these ionic compounds can be used alone or incombination of two or more thereof.

Further, by mixing LiBF₄ with a lithium salt having a perfluoroalkylgroup, such as LiN(C₂F₅SO₂)₂, the viscosity of the electrolyte can befurther reduced, so that the low-temperature characteristic can befurther improved, and self discharge can be suppressed, thus being moredesirable.

A ambient temperature molten salt or an ion liquid may be used as anonaqueous electrolyte.

The concentration of the electrolyte salt in the nonaqueous electrolyteis preferably 0.1 mol/l to 5 mol/l, further preferably 0.5 mol/l to 2.5mol/l for reliably obtaining a nonaqueous electrolyte battery havinghigh battery characteristics.

The negative electrode material is not limited, and may be freelyselected as long as it can precipitate or insert lithium ions. Examplesthereof include titanium-based materials such as lithium titanate havinga spinel-type crystal structure represented by Li[Li_(1/3)Ti_(5/3)]O₄,alloy-based materials such as Si-, Sb- and Sn-based alloy materials,lithium metal, lithium alloys (lithium metal-containing alloys such aslithium-silicon, lithium-aluminum, lithium-lead, lithium-tin,lithium-aluminum-tin, lithium-gallium and wood alloys), lithiumcomposite oxides (lithium-titanium) and silicon oxide as well as alloyscapable of insertion/extraction lithium, and carbon materials (e.g.graphite, hard carbon, low temperature-calcinated carbon and amorphouscarbon).

In the present invention, a powder of a positive active material has a50% particle size (D50) of 5 μm or less in particle size distributionmeasurement, but it is desirable that a powder of a negative electrodematerial have an average particle size of 100 μm or less. A crusher anda classifier are used for obtaining a powder in a predetermined shape.For example, a mortar, a ball mill, a sand mill, a vibration ball mill,a planet ball mill, a jet mill, a counter jet mill, a revolvingairflow-type jet mill, a sieve or the like is used. At the time ofcrushing, wet crushing can also be used in which water, or an organicsolvent such as hexane coexists. The classification method is notparticularly limited, a sieve, an air classifier or the like is used asnecessary in both dry and wet processes.

The positive active material and the negative electrode material whichare main components of the positive electrode and the negative electrodehave been described in detail above, but the aforementioned positiveelectrode and negative electrode may contain, in addition to theaforementioned main components, a conducting additive, a binding agent,a thickener, a filler and the like as other components.

The conducting additive is not limited as long as it is anelectron-conductive material that has no adverse effect on batteryperformance, but normally conductive materials such as natural graphite(scaly graphite, flake graphite, earthy graphite, etc.), artificialgraphite, carbon black, acetylene black, ketjen black, carbon whisker,carbon fibers, metal (copper, nickel, aluminum, silver, gold, etc.)powders, metal fibers and conductive ceramic materials can be includedalone or as a mixture thereof.

Among them, acetylene black is desirable as a conducting additive fromthe viewpoint of electron conductivity and coating properties. The addedamount of the conducting additive is preferably 0.1% by weight to 50% byweight, especially preferably 0.5% by weight to 30% by weight based onthe total weight of the positive electrode or negative electrode.Particularly, use of acetylene black crushed into ultrafine particles of0.1 to 0.5 μm is desirable because the required amount of carbon can bereduced. These mixing methods involve physical mixing, the ideal ofwhich is homogeneous mixing. Thus, mixing can be carried out in a dryprocess or a wet process using a powder mixer such as a V-type mixer, anS-type mixer, a grinder, a ball mill or a planet ball mill.

As the binding agent, thermoplastic resins such aspolytetrafluoroethylene (PTFE), polyvinylidene difluoride (PVDF),polyethylene and polypropylene, and polymers having rubber elasticity,such as ethylene-propylene-diene terpolymer (EPDM), sulfonated EPDM,styrene-butadiene rubber (SBR) and fluororubber can normally be usedalone or as a mixture of two or more thereof. The added amount of thebinding agent is preferably 1 to 50% by weight, especially preferably 2to 30% by weight based on the total weight of the positive electrode ornegative electrode.

The filler may be any material as long as it has no adverse effect onbattery performance. A polyolefin-based polymer such as polypropylene orpolyethylene, amorphous silica, alumina, zeolite, glass, carbon or thelike is normally used. The added amount of the filler is preferably 30%by weight or less based on the total amount of the positive electrode orthe negative electrode.

The positive electrode and the negative electrode are suitably preparedby mixing the aforementioned main components (positive active materialin the positive electrode and negative electrode material in thenegative electrode) and other materials to form a mixture, and mixingthe mixture with an organic solvent such as N-methylpyrrolidone ortoluene, followed by applying or contact-bonding the resulting mixedliquid onto a current collector that is described in detail below, andcarrying out a heating treatment at a temperature of about 50° C. to250° C. for about 2 hours. For the aforementioned coating method, forexample, it is desirable to perform coating in any thickness and anyshape using means such as roller coating by an applicator roll or thelike, screen coating, a doctor blade system, spin coating or a barcoater, but the applying method is not limited thereto.

As a separator, it is preferable that a porous membrane, a nonwovenfabric or the like, which shows excellent high-rate dischargeperformance, be used alone or in combination. Examples of the materialthat forms the separator for a nonaqueous electrolyte battery includepolyolefin-based resins represented by polyethylene, polypropylene andthe like, polyester-based resins represented by polyethyleneterephthalate, polybutyrene terephthalate and the like, polyvinylidenedifluoride, vinylidene fluoride-hexafluoropropylene copolymers,vinylidene fluoride-perfluoro vinyl ether copolymers, vinylidenefluoride-tetrafluoroethylene copolymers, vinylidenefluoride-trifluoroethylene copolymers, vinylidenefluoride-fluoroethylene copolymers, vinylidenefluoride-hexafluoroacetone copolymers, vinylidene fluoride-ethylenecopolymers, vinylidene fluoride-propylene copolymers, vinylidenefluoride-trifluoropropylene copolymers, vinylidenefluoride-tetrafluoroethylene-hexafluoropropylene copolymers andvinylidene fluoride-ethylene-tetrafluoroethylene copolymers.

The porosity of the separator is preferably 98% by volume or less fromthe viewpoint of the strength. The porosity is preferably 20% by volumeor more from the viewpoint of charge-discharge characteristics.

For the separator, for example, a polymer gel formed of acrylonitrile,ethylene oxide, propylene oxide, methyl methacrylate, vinyl acetate,vinyl pyrrolidone or a polymer such as polyfluoride vinylidene and anelectrolyte may be used. Use of the nonaqueous electrolyte in a gel formas described above is preferable from the viewpoint of being effectiveto prevent liquid leakage.

Further, for the separator, use of the above-mentioned porous membrane,nonwoven fabric or the like and the polymer gel in combination isdesirable because liquid retainability of the electrolyte is improved.That is, a film with the surface and the microporous wall face of apolyethylene microporous membrane coated with a solvophilic polymer in athickness of several μm or less, and an electrolyte is held withinmicropores of the film, so that the solvophilic polymer is formed into agel.

Examples of the solvophilic polymer include, in addition to polyfluoridevinylidene, polymers in which an acrylate monomer having an ethyleneoxide group, an ester group or the like, an epoxy monomer, a monomerhaving an isocyanate group, or the like is crosslinked. The monomer canbe subjected to a crosslinking reaction by carrying out heating or usingultraviolet rays (UV) while using a radical initiator at the same time,or using active light rays such as electron beams (EB), or the like.

The configuration of the lithium secondary battery is not particularlylimited, and examples thereof include a cylindrical battery, a prismaticbattery and a flat battery having a positive electrode, a negativeelectrode and a roll-shaped separator.

Both the conventional positive active material and the active materialof the present invention are capable of charge-discharge at a positiveelectrode potential of around 4.5 V (vs. Li/Li⁺). However, depending onthe type of a nonaqueous electrolyte used, battery performance may bedeterioration by oxidative decomposition of the nonaqueous electrolyteif the positive electrode potential during charge is too high.Therefore, a lithium secondary battery, with which a sufficientdischarge capacity is obtained even when such a charge method that themaximum potential of the positive electrode during charge is 4.3 V (vs.Li/Li⁺) or less is employed at the time of operation, may be required.If the active material of the present invention is used, a dischargeelectrical amount, which exceeds the capacity of the conventionalpositive active material, i.e. about 200 mAh/g or more can be obtainedeven when such a charge method that the maximum potential of thepositive electrode during charge is lower than 4.5 V (vs. Li/Li⁺), forexample 4.4 (vs. Li/Li⁺) or less or 4.3 (vs. Li/Li⁺) or less is employedat the time of operation

For the positive active material according to the present invention tohave a high discharge capacity, the ratio, at which transition metalelements that form a lithium transition metal composite oxide arepresent in areas other than transition metal sites of a layeredrock-salt-type crystal structure, is preferably low. This can beachieved by ensuring that in the precursor that is subjected to asintering step, transition metal elements such as Co, Ni and Mn in theprecursor core particles are sufficiently homogeneously distributed, andselecting suitable conditions for the sintering step for promotingcrystallization of an active material sample. If distribution oftransition metals in precursor core particles that are subjected to thesintering step is not homogeneous, a sufficient discharge capacity isnot obtained. The reason for this is not necessarily clear, but thepresent inventors think that this results from occurrence of so calledcation mixing in which the obtained lithium transition metal compositeoxide has some of transition metal elements present in areas other thantransition metal sites of the layered rock-salt-type crystal structure,i.e. lithium sites, if the distribution of transition metals inprecursor core particles that are subjected to the sintering step is nothomogeneous. A similar thought can be applied in a crystallizationprocess in the sintering step, wherein cation mixing in the layeredrock-salt-type crystal structure easily occurs if crystallization of theactive material sample is insufficient. Those in which the homogeneityof the distribution of the transition metal elements is high tend tohave a high intensity ratio of diffraction peaks of the (003) line andthe (104) line when the result of X-ray diffraction measurement isattributed to a space group R3-m. In the present invention, theintensity ratio of diffraction peaks of the (003) line and the (104)line from X-ray diffraction measurement is preferably I₍₀₀₃₎/I₍₁₀₄₎≧1.0.The intensity ratio is preferably I₍₀₀₃₎/I₍₁₀₄₎>1 at the end ofdischarge after charge-discharge. If synthesis conditions and synthesisprocedures for the precursor are inappropriate, the peak intensity ratiobecomes a smaller value, which is often less than 1.

By employing the synthesis conditions and synthesis procedures describedin the specification of the present application, a positive activematerial having high performance as described above can be obtained.Particularly, there can be provided a positive active material for alithium secondary battery with which a high discharge capacity can beobtained even when the charge upper limit potential is set to lower than4.5 (vs.Li/Li⁺), e.g. lower than 4.4 V (vs.Li/Li⁺) or 4.3 V (vs.Li/Li⁺).

EXAMPLE 1 EXAMPLE 1-1

Cobalt sulfate heptahydrate (14.08 g), nickel sulfate hexahydrate (21.00g) and manganese sulfate pentahydrate (65.27 g) were weighed, andtotally dissolved in 200 ml of ion-exchange water to prepare a 2.0 Maqueous sulfate solution of which the molar ratio of Co:Ni:Mn was12.50:19.94:67.56. 750 ml of ion exchange-water was poured into a 2 Lreaction tank, and a CO₂ gas was bubbled for 30 min to thereby dissolvethe CO₂ gas in ion-exchange water. The temperature of the reaction tankwas set at 50° C. (±2° C.), and the aqueous sulfate solution was addeddropwise at a rate of 3 ml/min while the contents in the reaction tankwas stirred at a rotation speed of 700 rpm using a paddle impellerequipped with a stirring motor. The control was performed so that pH inthe reaction tank was kept at 7.9 (±0.05) by appropriately addingdropwise an aqueous solution containing 1.0 M sodium carbonate, 1.0 Mlithium carbonate and 0.4 M ammonia during dropwise addition of theaqueous sulfate solution. After completion of dropwise addition,stirring the contents in the reaction tank was continued for further 3h. After stirring was stopped, the reaction tank was left standing for12 h or more.

Next, particles of a coprecipitation carbonate generated in the reactiontank were separated using a suction filtration device. Sodium ionsattached on the particles were further washed off under conditions ofperforming washing five times, with one-time washing includingperforming washing using 200 ml of ion-exchange water. The particleswere dried at 80° C. for 20 h under normal pressure in air atmosphereusing an electric furnace. Thereafter, the particles were crushed by anautomatic mortar made of agate for equalizing the particle size. In thisway, a coprecipitation carbonate precursor was prepared.

Lithium carbonate (0.970 g) was added to the coprecipitation carbonateprecursor (2.278 g), and the mixture was adequately mixed using anautomatic mortar made of agate to prepare a mixed powder of which themolar ratio of Li:(Co, Ni, Mn) was 130:100. The powder was molded at apressure of 6 MPa using a pellet molding machine to form a pellet havinga diameter of 25 mm. The amount of the mixed powder subjected to pelletmolding was determined by performing conversion calculation so that themass as an expected final product would be 2 g. One of the pellets wasplaced in an alumina boat having a total length of about 100 mm, theboat was placed in a box-type electric furnace (model: AMF 20), thetemperature was elevated from ordinary temperature to 900° C. undernormal pressure in an air atmosphere over 10 hours, and the pellet wassintered at 900° C. for 4 h. The box-type electric furnace had aninternal dimension of 10 cm (height), 20 cm (width) and 30 cm (depth),and provided with electrically heated wires at intervals of 20 cm in thewidth direction. After calcination, a heater was switched off, thealumina boat was naturally cooled as it was left standing in thefurnace. As a result, the temperature of the furnace decreased to about200° C. after 5 hours, but the subsequent temperature fall rate wasslightly low. After elapse of a whole day and night, the pellet wastaken out after confirming that the temperature of the furnace was nothigher than 100° C., and crushed by an automatic mortar made of agatefor equalizing the particle size. In this way, a lithium transitionmetal composite oxide Li_(1.13)Co_(0.11)Ni_(0.17)Mn_(0.59)O₂ containingNa according to Example 1-1 was prepared.

EXAMPLES 1-2 TO 1-6

Lithium transition metal composite oxides containing Na according toExamples 1-2 to 1-6 were prepared in the same manner as in Example 1-1except that the molar ratio (molar ratio of Na/Li) of sodium carbonateand lithium carbonate contained in an aqueous solution that was addeddropwise when a coprecipitation carbonate precursor was prepared was not1/1 [M] but changed as described in Examples 1-2 to 1-6 in Table 1.

EXAMPLE 1-7

Cobalt sulfate heptahydrate (14.08 g), nickel sulfate hexahydrate (21.00g) and manganese sulfate pentahydrate (65.27 g) were weighed, andtotally dissolved in 200 ml of ion-exchange water to prepare a 2.0 Maqueous sulfate solution of which the molar ratio of Co:Ni:Mn was12.50:19.94:67.56. 750 ml of ion exchange-water was poured into a 2 Lreaction tank, and a CO₂ gas was bubbled for 30 min to thereby dissolvethe CO₂ gas in ion-exchange water. The temperature of the reaction tankwas set at 50° C. (±2° C.), and the aqueous sulfate solution was addeddropwise at a rate of 3 ml/min while the contents in the reaction tankwas stirred at a rotation speed of 700 rpm using a paddle impellerequipped with a stirring motor. Here, the control was performed so thatpH in the reaction tank was kept at 7.9 (±0.05) by appropriately addingdropwise an aqueous solution containing 2.0 M sodium carbonate and 0.4 Mammonia during dropwise addition of the aqueous sulfate solution. Aftercompletion of dropwise addition, stirring the contents in the reactiontank was continued for further 3 h. After stirring was stopped, thereaction tank was left standing for 12 h or more.

Next, particles of a coprecipitation carbonate generated in the reactiontank were separated using a suction filtration device, sodium ionsattached on the particles were further washed off under conditions ofperforming washing five times, with one-time washing includingperforming washing using 200 ml of ion-exchange water, and the particleswere dried at 80° C. for 20 h under normal pressure in air atmosphereusing an electric furnace. Thereafter, the particles were crushed by anautomatic mortar made of agate for equalizing the particle size. In thisway, a coprecipitation carbonate precursor was prepared.

Lithium carbonate (0.970 g) and sodium carbonate (0.005 g) were added tothe coprecipitation carbonate precursor (2.278 g), and the mixture wasadequately mixed using an automatic mortar made of agate to prepare amixed powder of which the molar ratio of Li:(Co, Ni, Mn) was 130:100.The powder was molded at a pressure of 6 MPa using a pellet moldingmachine to form a pellet having a diameter of 25 mm. The amount of themixed powder subjected to pellet molding was determined by performingconversion calculation so that the mass as an expected final productwould be 2 g. One of the pellets was placed in an alumina boat having atotal length of about 100 mm, the boat was placed in a box-type electricfurnace (model: AMF 20), the temperature was elevated from ordinarytemperature to 900° C. under normal pressure in air atmosphere over 10hours, and the pellet was sintered at 900° C. for 4 h. The box-typeelectric furnace had an internal dimension of 10 cm (height), 20 cm(width) and 30 cm (depth), and provided with electrically heated wiresat intervals of 20 cm in the width direction. After calcination, aheater was switched off, the alumina boat was naturally cooled as it wasleft standing in the furnace. As a result, the temperature of thefurnace decreased to about 200° C. after 5 hours, but the subsequenttemperature fall rate was slightly low. After elapse of a whole day andnight, the pellet was taken out after confirming that the temperature ofthe furnace was not higher than 100° C., and crushed by an automaticmortar made of agate for equalizing the particle size. In this way, alithium transition metal composite oxideLi_(1.13)Co_(0.11)Ni_(0.17)Mn_(0.59)O₂ containing Na according toExample 1-7 was prepared.

EXAMPLES 1-8 TO 1-14 and Comparative Example 1-1

Lithium transition metal composite oxides containing Na according toExamples 1-8 to 1-10 and Comparative Example 1-1 were prepared in thesame manner as in Example 1-7 except that the amount of sodium carbonateadded to the coprecipitation carbonate precursor (2.278 g) together withlithium carbonate (0.970 g) was changed to 0.018 g in Example 1-8, 0.023g in Example 1-9, 0.046 g in Example 1-10 and 0.069 g in ComparativeExample 1-1.

Lithium transition metal composite oxides containing Na according toExamples 1.11 to 1-14 were prepared in the same manner as in Example 1-7except that to the coprecipitation carbonate precursor (2.278 g) wasadded lithium carbonate (0.969 g), and the amount of sodium carbonateadded therewith was changed to 0.0599 g in Example 1-11, 0.0645 g inExample 1-12, 0.0691 g in Example 1.13 and 0.0737 g in Example 1-14.

EXAMPLES 1-15 TO 1-19

Lithium transition metal composite oxides containing Na according toExamples 1-15 to 1-19 were each prepared in the same manner as inExamples 1.1 to 1-5 except that the sintering temperature was changedfrom 900° C. to 850° C.

EXAMPLES 1-20 TO 1-24

Lithium transition metal composite oxides containing Na according toExamples 1-20 to 1-24 were each prepared in the same manner as inExamples 1-1 to 1-5 except that the sintering temperature was changedfrom 900° C. to 800° C.

EXAMPLES 1-25 TO 1-30

Lithium transition metal composite oxidesLi_(1.17)Co_(0.10)Ni_(0.17)Mn_(0.56)O₂ containing Na according toExamples 1-25 to 1-30 were each prepared in the same manner as inExamples 1-1 to 1-6 except that the molar ratio of Li/Me (Co, Ni, Mn)was changed from 1.3 to 1.4 (coprecipitation carbonate precursor:lithiumcarbonate=2.228 g:1.021 g).

EXAMPLE 1-31

A lithium transition metal composite oxide containing Na according toExample 1-31 was prepared in the same manner as in Example 1-25 exceptthat the time over which contents in the reaction tank were furthercontinuously stirred after completion of dropwise addition in the stepof preparing a coprecipitation carbonate precursor was changed from 3 hto 4 h.

EXAMPLES 1-32 TO 1-39

Lithium transition metal composite oxidesLi_(1.17)Co_(0.10)Ni_(0.17)Mn_(0.56)O₂ containing Na according toExamples 1-32 to 1-39 were prepared in the same manner as in Example 1-7except that for changing the molar ratio of Li/Me (Co, Ni, Mn) from 1.3to 1.4, 1.021 g of lithium carbonate was added to 2.228 g of thecoprecipitation carbonate precursor, and the amount of sodium carbonateadded therewith was changed to 0.0138 g in Example 1-32, 0.0277 g inExample 1-33, 0.0320 g in Example 1-34, 0.0553 g in Example 1-35, 0.0599g in Example 1-36, 0.0645 g in Example 1-37, 0.0691 g in Example 1-38and 0.0737 g in Example 1-39.

EXAMPLES 1-40 TO 1-46

Lithium transition metal composite oxidesLi_(1.11)Co_(0.11)Ni_(0.18)Mn_(0.60)O₂ containing Na according toExamples 1-40 to 1-46 were prepared in the same manner as in Example 1-7except that for changing the molar ratio of Li/Me (Co, Ni, Mn) from 1.3to 1.25, 0.942 g of lithium carbonate was added to 2.304 g of thecoprecipitation carbonate precursor, and the amount of sodium carbonateadded therewith was changed to 0.0138 g in Example 1-40, 0.0277 g inExample 1-41, 0.0320 g in Example 1-42, 0.0553 g in Example 1-43, 0.0599g in Example 1-44, 0.0645 g in Example 1-45 and 0.0691 g in Example1-46.

EXAMPLES 1-47 TO 1-53

Lithium transition metal composite oxidesLi_(1.184)Co_(0.102)Ni_(0.163)Mn_(0.551)O₂ containing Na according toExamples 1-47 to 1-53 were prepared in the same manner as in Example 1-7except that for changing the molar ratio of Li/Me (Co, Ni, Mn) from 1.3to 1.45, 1.046 g of lithium carbonate was added to 2.203 g of thecoprecipitation carbonate precursor, and the amount of sodium carbonateadded therewith was changed to 0.0138 g in Example 1-47, 0.0277 g inExample 1-48, 0.0320 g in Example 1-49, 0.0553 g in Example 1-50, 0.0599g in Example 1-51, 0.0645 g in Example 1-52 and 0.0691 g in Example1-53.

COMPARATIVE EXAMPLES 1-2 TO 1-6

Lithium transition metal composite oxides according to ComparativeExamples 1-2 to 1-6 were prepared in the same manner as in Example 1-1except that the ratio (molar ratio of Na/Li) of sodium carbonate andlithium carbonate contained in an aqueous solution that was addeddropwise when a coprecipitation carbonate precursor was prepared was not1/1 [M] but changed as described in Comparative Examples 1-2 to 1-6 inTable 1 (no sodium carbonate in Comparative Example 1-6).

COMPARATIVE EXAMPLE 1-7

A lithium transition metal composite oxide according to ComparativeExample 1-7 was prepared in the same manner as in Example 1-1 exceptthat potassium carbonate was contained, in place of sodium carbonate andlithium carbonate in an aqueous solution that was added dropwise when acoprecipitation carbonate precursor was prepared.

COMPARATIVE EXAMPLE 1-8

A lithium transition metal composite oxide according to ComparativeExample 1-8 was prepared in the same manner as in Example 1-1 exceptthat ammonium hydrogen carbonate was contained, in place of sodiumcarbonate and lithium carbonate in an aqueous solution that was addeddropwise when a coprecipitation carbonate precursor was prepared.

COMPARATIVE EXAMPLE 1-9

A lithium transition metal composite oxide according to ComparativeExample 1-9 was prepared in the same manner as in Example 1-5 exceptthat the composition was changed fromLi_(1.13)Co_(0.11)Ni_(0.17)Mn_(0.59)O₂ to LiCo_(1/3)Ni_(1/3)Mn_(1/3)O₂.

COMPARATIVE EXAMPLE 1-10

A lithium transition metal composite oxide according to ComparativeExample 1-10 was prepared in the same manner as in Comparative Example1-6 except that the composition was changed fromLi_(1.13)Co_(0.11)Ni_(0.17)Mn_(0.59)O₂ to LiCo_(1/3)Ni_(1/3)Mn_(1/3)O₂.

(Measurement of the Amount of Na Contained in Lithium Transition MetalComposite Oxide)

The amount of Na contained in the obtained lithium transition metalcomposite oxide was determined in the following manner. An activematerial (50 mg) was weighed, and put in 10 ml of a 10 wt % aqueoushydrochloric acid solution. By heating the aqueous solution on a hotplate at 150° C., the active material was sufficiently dissolved.Thereafter, the aqueous solution was filtered using a suction filtrationdevice to remove fine particles contained in the aqueous solution.Ion-exchange water (90 ml) was added to the aqueous solution afterfiltration, and the resulting mixture was stirred to prepare 100 ml of asample solution. Three reference solutions having known Naconcentrations were prepared for creating a calibration curve fordetermining a Na content. The reference solution was prepared bydiluting a Na standard solution (manufactured by Nacalai Tesque, Inc.;1000 ppm) to a desired concentration using ion-exchange water.

The Na content was measured by performing an analysis with an ICPemission spectrophotometer (SHIMADZU, ICPS-8100) using about 20 to 40 mlof each of the sample solution and the reference solution.

The amount of Na contained in the lithium transition metal compositeoxide can be measured by atomic absorption spectroscopy aside from theICP emission spectroscopic analysis described above.

(Measurement of Particle Size)

For the lithium transition metal composite oxides according to Examples1-1 to 1-53 and Comparative Examples 1-1 to 1-10, particle sizedistribution measurements were made in accordance with the followingconditions and procedure. Microtrac (model: MT 3000) manufactured byNikkiso Co., Ltd. was used as a measuring apparatus. The measuringapparatus includes an optical stage, a sample supply section and acomputer including control software, and a wet cell having a laser lighttransmission window is placed on the optical stage. For the measurementprinciple, a wet cell, through which a dispersion with a measurementobject sample dispersed in a dispersive solvent is circulated, isirradiated with laser light, and a distribution of scattered light fromthe measurement sample is converted into a particle size distribution.The dispersion is stored in a sample supply section, and cyclicallysupplied to the wet cell by a pump. The sample supply section constantlyreceives ultrasonic vibrations. In this measurement, water was used as adispersive solvent. Microtrac DHS for Win 98 (MT 3000) was used asmeasurement control software. For “substance information” set and inputin the measuring apparatus, a value of 1.33 was set as the “refractiveindex” of the solvent, “Transparent” was selected as the “transparency”,and “Nonspherical” was selected as the “spherical particle”. A “SetZero” operation is performed prior to measurement of the sample. The“Set Zero” operation is an operation for subtracting influences onsubsequent measurements of disturbance factors (glass, contamination ofthe glass wall face, glass irregularities, etc.) other than scatteredlight from particles, wherein only water as a dispersive solvent is fedin a sample supply section, a background operation is performed withonly water as a dispersive solvent being circulated through a wet cell,and background data is stored in a computer. Subsequently, a “Sample LD(Sample Loading)” operation is performed. The Sample LD operation is anoperation for optimizing the concentration of a sample in a dispersionthat is cyclically supplied to a wet cell during measurement, wherein ameasurement object sample is manually introduced into a sample supplysection in accordance with instructions of measurement control softwareuntil an optimum amount is reached. Subsequently, a “measurement” buttonis depressed, so that a measurement operation is performed. Themeasurement operation is repeated twice and as an average thereof, ameasurement result is output from a computer. The measurement result isacquired as a particle size distribution histogram, and the values ofD10, D50 and D90 (D10, D50 and D90 are particle sizes at which thecumulative volume in the particle size distribution of secondaryparticles is 10%, 50% and 90%, respectively. Values of D50 measured areshown in Table 1 as “D50 particle size (μm)”.

The cumulative volume in the particle size distribution of secondaryparticles of the carbonate precursor was comparable to that of thelithium transition metal composite oxide.

(Pore Volume Distribution Measurement)

For the lithium transition metal composite oxides according to Examples1-5, 1-24 and 1-29, pore volume distribution measurements were made inaccordance with the following conditions and procedure. For measurementof the pore volume distribution, “Autosorb iQ” and control/analysissoftware “ASiQwin” manufactured by Quantachrome Instruments were used. Alithium transition metal composite oxide (1.00 g) as a sample to bemeasured was placed in a sample tube for measurement, and vacuum-driedat 120° C. for 12 h to sufficiently remove moisture in the measurementsample. Next, by a nitrogen gas adsorption method using liquid nitrogen,isotherms on the adsorption side and the desorption side were measuredat a relative pressure P/P0 (P0=about 770 mmHg) ranging from 0 to 1.Then, a pore distribution was evaluated by performing a calculation byBJH method using the isotherm on the desorption side.

In the lithium transition metal composite oxides according to Examples1-5, 1-24 and 1-29, the pore sizes, at which the differential porevolume determined by BJH method from an adsorption isotherm obtainedusing a nitrogen gas adsorption method shows a maximum value, were in arange of 30 to 40 nm, and the peak differential pore volumes were 1.39mm³/(g·nm), 1.76 mm³/(g·nm) and 0.85 mm³/(g·nm), respectively.

(Assembling and Evaluation of Lithium Secondary Battery)

A lithium secondary battery was assembled by the following procedureusing the lithium transition metal composite oxide of each of Examples1-1 to 1-53 and Comparative Examples 1-1 to 1-10 as a positive activematerial for a lithium secondary battery, and battery characteristicswere evaluated.

A applying paste was prepared in which the active material, acetyleneblack (AB) and polyvinylidene fluoride (PVdF) were mixed at a ratio of90:5:5 in terms of a weight ratio and dispersed with N-methylpyrrolidoneas a dispersion medium. The applying paste was applied to one surface ofan aluminum foil current collector having a thickness of 20 μm toprepare a positive electrode plate. The mass and coating thickness ofthe active material coated per fixed area were equalized so that testconditions were the same among the lithium secondary batteries of allExamples and Comparative Examples.

For the purpose of accurately observing the independent behavior of apositive electrode, metallic lithium was brought into close contact witha nickel foil current collector and used for a counter electrode, i.e. anegative electrode. Here, a sufficient amount of metallic lithium wasplaced on the negative electrode so that the capacity of the lithiumsecondary battery was not limited by the negative electrode.

As an electrolyte solution, a solution obtained by dissolving LiPF₆, ina concentration of 1 mol/l, in a mixed solvent of ethylene carbonate(EC)/ethylmethyl carbonate (EMC)/dimethyl carbonate (DMC) in a volumeratio of 6:7:7, was used. As a separator, a microporous membrane made ofpolypropylene, the surface of which was modified with polyacrylate, wasused. As a sheath, a metal resin composite film made of polyethyleneterephthalate (15 μm)/aluminum foil (50 μm)/metal-adhesive polypropylenefilm (50 μm) was used. The electrode was stored such that the open endsof a positive electrode terminal and a negative electrode terminal wereexternally exposed. Fusion margins with the inner surfaces of theaforementioned metal resin composite films facing each other wereairtightly sealed except a portion forming an electrolyte solutionfilling hole. The electrolyte solution was injected, followed by sealingthe electrolyte solution filling hole.

The lithium secondary battery assembled in the procedure described abovewas subjected to an initial charge-discharge step at 25° C. Charge wasconstant current-constant voltage charge with a current of 0.1 CA and avoltage of 4.6 V, and the charge termination condition was set at a timepoint at which the current value decreased to ⅙. Discharge was constantcurrent discharge with a current of 0.1 CA and a final voltage of 2.0 V.This charge-discharge was carried out 2 cycles. Here, a rest step of 30minutes was provided each after charge and after discharge.

Next, a 1 cycle charge-discharge test was conducted with the chargevoltage changed. Voltage control was all performed for the positiveelectrode potential. Conditions for the charge-discharge test are thesame as the conditions for the initial charge-discharge step except thatthe charge voltage is 4.3 V. The discharge capacity at this time wasrecorded as a “discharge capacity (mAh/g)” (described as “0.1 C capa” inthe table).

The test results for the lithium secondary battery using the lithiumtransition metal composite oxide according to each of Examples 1-1 to1-53 and Comparative Examples 1-1 to 1-10 as a positive active materialfor a lithium secondary battery are shown in Tables 1 and 2.

TABLE 1 D50 Li/Me Sintering particle molar temperature size 0.1 C capaNeutralizer ratio (° C.) Na (ppm) (μm) (mAh/g) Example 1-1 Na/Li =1/1[M] 1.3 900 1000 8 215 Example 1-2 Na/Li = 1.3/0.7[M] ↑ ↑ 1200 8 220Example 1-3 Na/Li = 1.6/0.4[M] ↑ ↑ 1500 8 224 Example 1-4 Na/Li =1.9/0.1[M] ↑ ↑ 1800 8 228 Example 1-5 Na₂CO₃ 2[M] ↑ ↑ 2100 8 226 Example1-6 Na/Li = 0.85/1.15[M] ↑ ↑ 900 8 197 Example 1-7 Na₂CO₃ 2[M] + Naadded ↑ ↑ 3000 8 230 Example 1-8 ↑ ↑ ↑ 6000 8 236 Example 1-9 ↑ ↑ ↑ 70008 234 Example 1-10 ↑ ↑ ↑ 12000 8 226 Example 1-11 ↑ ↑ ↑ 13000 8 221Example 1-12 ↑ ↑ ↑ 14000 8 211 Example 1-13 ↑ ↑ ↑ 15000 8 193 Example1-14 ↑ ↑ ↑ 16000 8 185 Comparative ↑ ↑ ↑ 17000 8 178 Example 1-1 Example1-15 Na/Li = 1/1[M] ↑ 850 1000 8 213 Example 1-16 Na/Li = 1.3/0.7[M] ↑ ↑1200 8 219 Example 1-17 Na/Li = 1.6/0.4[M] ↑ ↑ 1500 8 223 Example 1-18Na/Li = 1.9/0.1[M] ↑ ↑ 1800 8 225 Example 1-19 Na₂CO₃ 2[M] ↑ ↑ 2100 8225 Example 1-20 Na/Li = 1/1[M] ↑ 800 1000 8 208 Example 1-21 Na/Li =1.3/0.7[M] ↑ ↑ 1200 8 210 Example 1-22 Na/Li = 1.6/0.4[M] ↑ ↑ 1500 8 210Example 1-23 Na/Li = 1.9/0.1[M] ↑ ↑ 1800 8 212 Example 1-24 Na₂CO₃ 2[M]↑ ↑ 2100 8 213 Example 1-25 Na/Li = 1/1[M] 1.4 900 1000 8 212 Example1-26 Na/Li = 1.3/0.7[M] ↑ ↑ 1200 8 215 Example 1-27 Na/Li = 1.6/0.4[M] ↑↑ 1500 8 218 Example 1-28 Na/Li = 1.9/0.1[M] ↑ ↑ 1800 8 220 Example 1-29Na₂CO₃ 2[M] ↑ ↑ 2100 8 220 Example 1-30 Na/Li = 0.85/1.15[M] ↑ ↑ 900 8195 Example 1-31 Na/Li = 1/1[M] ↑ ↑ 1000 10 214

TABLE 2 D50 Li/Me Sintering particle molar temperature size 0.1 C capaNeutralizer ratio (° C.) Na (ppm) (μm) (mAh/g) Example 1-32 Na₂CO₃2[M] + Na added 1.4 900 3000 8 222 Example 1-33 ↑ ↑ ↑ 6000 8 224 Example1-34 ↑ ↑ ↑ 7000 8 224 Example 1-35 ↑ ↑ ↑ 12000 8 222 Example 1-36 ↑ ↑ ↑13000 8 220 Example 1-37 ↑ ↑ ↑ 14000 8 220 Example 1-38 ↑ ↑ ↑ 15000 8212 Example 1-39 ↑ ↑ ↑ 16000 8 203 Example 1-40 ↑ 1.25 ↑ 3000 8 210Example 1-41 ↑ ↑ ↑ 6000 8 213 Example 1-42 ↑ ↑ ↑ 7000 8 213 Example 1-43↑ ↑ ↑ 12000 8 211 Example 1-44 ↑ ↑ ↑ 13000 8 210 Example 1-45 ↑ ↑ ↑14000 8 205 Example 1-46 ↑ ↑ ↑ 15000 8 201 Example 1-47 ↑ 1.45 ↑ 3000 8209 Example 1-48 ↑ ↑ ↑ 6000 8 212 Example 1-49 ↑ ↑ ↑ 7000 8 213 Example1-50 ↑ ↑ ↑ 12000 8 213 Example 1-51 ↑ ↑ ↑ 13000 8 214 Example 1-52 ↑ ↑ ↑14000 8 214 Example 1-53 ↑ ↑ ↑ 15000 8 212 Comparative Na/Li =0.7/1.3[M] 1.4 900 800 8 179 Example 1-2 Comparative Na/Li = 0.5/1.5[M]↑ ↑ 600 8 175 Example 1-3 Comparative Na/Li = 0.3/1.7[M] ↑ ↑ 400 8 168Example 1-4 Comparative Na/Li = 0.1/1.9[M] ↑ ↑ 200 8 163 Example 1-5Comparative Li₂CO₃ 2[M] ↑ ↑ 100 8 162 Example 1-6 Comparative K₂CO₃ 2[M]↑ ↑ 100 8 170 Example 1-7 Comparative NH₄HCO₃ 2[M] ↑ ↑ 100 8 156 Example1-8 Comparative Na₂CO₃ 2[M] 1.0 900 2100 8 153 Example 1-9 ComparativeLi₂CO₃ 2[M] 1.0 ↑ 100 8 155 Example 1-10

It is apparent from Tables 1 and 2 that lithium secondary batteriesusing the positive active materials of Examples 1-1 to 1-53, in whichthe Li/Me ratio of the lithium transition metal composite oxide is 1.25to 1.45, Na is contained in an amount of 900 to 16000 ppm, and the D50particle size is 8 to 10 μm, have a high discharge capacity with thedischarge capacity (0.1 C capa) being 180 mAh/g or more, andparticularly those containing Na in an amount of 1000 to 14000 ppm havea discharge capacity (0.1 C capa) of 200 mAh/g or more.

On the other hand, lithium secondary batteries using the positive activematerials in which the Li/Me ratio is 1.25 to 1.45, but the content ofNa is less than 900 ppm for Comparative Examples 1-2 to 1-8 and thecontent of Na is more than 16000 ppm for Comparative Example 1-1 have adischarge capacity (0.1 C capa) of less than 180 mAh/g, and improvementof the discharge capacity is not sufficient.

The lithium secondary battery using a positive active material(LiCo_(1/3)Ni_(1/3)Mn_(1/3)O₂), which is not of so called a“lithium-excess-type” but of so called a “LiMeO₂-type”, has a dischargecapacity (0.1 C capa) of only 153 mAh/g, although the content of Na is2100 ppm, as shown in Comparative Example 1-9. Moreover, since thelithium secondary battery of Comparative Example 1-9 described above hasa discharge capacity comparable to that of the lithium secondary batteryof Comparative Example 1-10 using a positive active material of the same“LiMeO₂-type” in which the content of Na is 100 ppm, such an effect thatthe discharge capacity is significantly improved by including Na in aspecified amount may be specific to the “lithium-excess-type” positiveactive material.

EXAMPLE 2 EXAMPLE 2-1

Cobalt sulfate heptahydrate (14.08 g), nickel sulfate hexahydrate (21.00g) and manganese sulfate pentahydrate (65.27 g) were weighed, andtotally dissolved in 200 ml of ion-exchange water to prepare a 2.0 Maqueous sulfate solution of which the molar ratio of Co:Ni:Mn was12.50:19.94:67.56. 750 ml of ion exchange-water was poured into a 2 Lreaction tank, and a CO₂ gas was bubbled for 30 min to thereby dissolvethe CO₂ gas in ion-exchange water. The temperature of the reaction tankwas set at 50° C. (±2° C.), and the aqueous sulfate solution was addeddropwise at a rate of 3 ml/min while the contents in the reaction tankwas stirred at a rotation speed of 700 rpm using a paddle impellerequipped with a stirring motor. Here, the control was performed so thatpH in the reaction tank was kept at 7.9 (±0.05) by appropriately addingdropwise an aqueous solution containing 2.0 M potassium carbonate and0.4 M ammonia during dropwise addition of the aqueous sulfate solution.After completion of dropwise addition, stirring the contents in thereaction tank was continued for further 3 h. After stirring was stopped,the reaction tank was left standing for 12 h or more.

Next, particles of a coprecipitation carbonate generated in the reactiontank were separated using a suction filtration device. Potassium ionsattached on the particles were further washed off under conditions ofperforming washing five times, with one-time washing includingperforming washing using 200 ml of ion-exchange water. The particleswere dried at 80° C. for 20 h under normal pressure in air atmosphereusing an electric furnace. Thereafter, the particles were crushed by anautomatic mortar made of agate for equalizing the particle size. In thisway, a coprecipitation carbonate precursor was prepared.

Lithium carbonate (0.970 g) and potassium carbonate (0.004 g) were addedto the coprecipitation carbonate precursor (2.278 g), and the mixturewas adequately mixed using an automatic mortar made of agate to preparea mixed powder of which the molar ratio of Li=(Co, Ni, Mn) was 130:100.The powder was molded at a pressure of 6 MPa using a pellet moldingmachine to form a pellet having a diameter of 25 mm. The amount of themixed powder subjected to pellet molding was determined by performingconversion calculation so that the mass as an expected final productwould be 2 g. One of the pellets was placed in an alumina boat having atotal length of about 100 mm, the boat was placed in a box-type electricfurnace (model: AMF 20), the temperature was elevated from ordinarytemperature to 900° C. under normal pressure in an air atmosphere over10 hours, and the pellet was sintered at 900° C. for 4 h. The box-typeelectric furnace had an internal dimension of 10 cm (height), 20 cm(width) and 30 cm (depth), and provided with electrically heated wiresat intervals of 20 cm in the width direction. After calcination, aheater was switched off, and the alumina boat was naturally cooled as itwas left standing in the furnace. As a result, the temperature of thefurnace decreased to about 200° C. after 5 hours, but the subsequenttemperature fall rate was slightly low. After elapse of a whole day andnight, the pellet was taken out after confirming that the temperature ofthe furnace was not higher than 100° C., and crushed by an automaticmortar made of agate for equalizing the particle size. In this way, alithium transition metal composite oxideLi_(1.13)Co_(0.11)Ni_(0.17)Mn_(0.59)O₂ containing K according to Example2-1 was prepared.

EXAMPLES 2-2 TO 2-10

Lithium transition metal composite oxides containing K according toExamples 2-2 to 2-8 were prepared in the same manner as in Example 2qexcept that the amount of potassium carbonate added to thecoprecipitation carbonate precursor (2.278 g) together with lithiumcarbonate (0.970 g) was changed to 0.011 g in Example 2-2, 0.018 g inExample 2-3, 0.032 g in Example 2-4, 0.050 g in Example 2-5, 0.054 g inExample 2-6, 0.057 g in Example 2-7 and 0.060 g in Example 2-8.

Lithium transition metal composite oxides containing K according toExamples 2-9 and 2-10 were prepared in the same manner as in Example 2-1except that to the coprecipitation carbonate precursor (2.278 g) wasadded lithium carbonate (0.969 g), and the amount of potassium carbonateadded therewith was changed to 0.0043 g in Example 2-9 and 0.0053 g inExample 2-10.

EXAMPLES 2-11 TO 2-17

Lithium transition metal composite oxides containing K according toExamples 2-11 to 2-17 were each prepared in the same manner as inExamples 2-1 to 2-7 except that the sintering temperature was changedfrom 900° C. to 800° C.

EXAMPLES 2-18 TO 2-27

Lithium transition metal composite oxidesLi_(1.17)Co_(0.10)Ni_(0.17)Mn_(0.56)O₂ containing K according toExamples 2-18 to 2-27 were each prepared in the same manner as inExamples 2-1 to 2-10 except that the molar ratio of Li/Me (Co, Ni, Mn)was changed from 1.3 to 1.4 (coprecipitation carbonate precursor:lithiumcarbonate=2.228 g:1.021 g).

EXAMPLES 2-28 TO 2-32

Lithium transition metal composite oxidesLi_(1.11)Co_(0.11)Ni_(0.18)Mn_(0.60)O₂ containing K according toExamples 2.28 to 2-32 were each prepared in the same manner as inExamples 2-1 to 2-5 except that for changing the molar ratio of Li/Me(Co, Ni, Mn) from 1.3 to 1.25, lithium carbonate (0.942 g) was added tothe coprecipitation carbonate precursor (2.304 g), and the amount ofpotassium carbonate added therewith was changed to 0.0071 g in Example2-28, 0.0142 g in Example 2-29, 0.0213 g in Example 2-30, 0.0354 g inExample 2-31 and 0.0532 g in Example 2-32.

EXAMPLES 2-33 TO 2-37

Lithium transition metal composite oxidesLi_(1.184)Co_(0.102)Ni_(0.163)Mn_(0.551)O₂ containing K according toExamples 2-33 to 2-37 were prepared in the same manner as in Examples2-1 to 2-5 except that for changing the molar ratio of Li/Me (Co, Ni,Mn) from 1.3 to 1.45, lithium carbonate (1.046 g) was added to thecoprecipitation carbonate precursor (2.203 g), and the amount ofpotassium carbonate added therewith was changed to 0.0071 g in Example2-33, 0.0142 g in Example 2-34, 0.0213 g in Example 2-35, 0.0354 g inExample 2-36 and 0.0532 g in Example 2-37.

COMPARATIVE EXAMPLES 2-1 AND 2-2

Lithium transition metal composite oxides containing K according toComparative Examples 2-1 and 2-2 were prepared in the same manner as inExample 2-1 except that the amount of potassium carbonate added to 2.278g of the coprecipitation carbonate precursor together with 0.970 g oflithium carbonate was changed to 0.064 g in Comparative Example 2-1 and0.067 g in Comparative Example 2-2.

COMPARATIVE EXAMPLES 2-3 AND 2-4

Lithium transition metal composite oxides containing K according toComparative Examples 2-3 and 2-4 were each prepared in the same manneras in Comparative Examples 2-1 and 2-2 except that the sinteringtemperature was changed from 900° C. to 800° C.

COMPARATIVE EXAMPLES 2-5 AND 2-6

Lithium transition metal composite oxides containing K according toComparative Examples 2-5 and 2-6 were prepared in the same manner as inExample 2-18 except that the amount of potassium carbonate added to2.228 g of the coprecipitation carbonate precursor together with 1.021 gof lithium carbonate was changed to 0.064 g in Comparative Example 2.5and 0.067 g in Comparative Example 2-6.

COMPARATIVE EXAMPLE 2-7

A lithium transition metal composite oxide containing K according toComparative Example 2-7 was prepared in the same manner as in Example2-1 except that potassium carbonate was not added but only 0.970 g oflithium carbonate was added to 2.278 g of the coprecipitation carbonateprecursor.

COMPARATIVE EXAMPLES 2-8 TO 2-10

Lithium transition metal composite oxides according to ComparativeExamples 2-8 to 2-10 were prepared in the same manner as in Example 2-1except a change was made such that in an aqueous solution that was addeddropwise when a precipitation carbonate precursor was prepared,potassium carbonate and lithium carbonate were contained in place of 2.0M potassium carbonate (K/Li=1/1 [M] in Comparative Example 2-8;K/Li=0.5/1.5 [M] in Comparative Example 2-9), and potassium carbonatewas not contained but 2.0 M lithium carbonate was contained (ComparativeExample 2-10).

COMPARATIVE EXAMPLE 2-11

A lithium transition metal composite oxide according to ComparativeExamples 2-11 was prepared in the same manner as in Example 2-1 exceptthat ammonium hydrogen carbonate was contained, in place of potassiumcarbonate, in an aqueous solution that was added dropwise when acoprecipitation carbonate precursor was prepared.

COMPARATIVE EXAMPLE 2-12

A lithium transition metal composite oxide containing K according toComparative Example 2-12 was prepared in the same manner as in Example2-1 except that the composition was changed fromLi_(1.13)Co_(0.11)Ni_(0.17)Mn_(0.59)O₂ to LiCo_(1/3)Ni_(1/3)Mn_(1/3)O₂.

COMPARATIVE EXAMPLE 2-13

A lithium transition metal composite oxide according to ComparativeExample 2-13 was prepared in the same manner as in Comparative Example2-10 except that the composition was changed fromLi_(1.13)Co_(0.11)Ni_(0.17)Mn_(0.59)O₂ to LiCo_(1/3)Ni_(1/3)Mn_(1/3)O₂.

(Measurement of the Amount of K Contained in Lithium Transition MetalComposite Oxide)

The amount of K contained in the obtained lithium transition metalcomposite oxide was determined by performing an analysis with an ICPemission spectrophotometer (SHIMADZU, ICPS-8100) as in the measurementof the amount of Na.

(Measurement of Particle Size)

For the lithium transition metal composite oxides according to Examples2-1 to 2-37 and Comparative Examples 2-1 to 2-13, particle sizedistribution measurements were made in the same manner as in themeasurement for the lithium transition metal composite oxide accordingto Example 1. Values of D50 measured were all 8 μm.

(Assembling and Evaluation of Lithium Secondary Battery)

A lithium secondary battery was assembled in the same manner as inExample 1 using the lithium transition metal composite oxide of each ofExamples 2-1 to 2-37 and Comparative Examples 2-1 to 2-13 as a positiveactive material for a lithium secondary battery, and batterycharacteristics were evaluated.

The test results for the lithium secondary battery using the lithiumtransition metal composite oxide according to each of Examples 2-1 to2-37 and Comparative Examples 2-1 to 2-13 as a positive active materialfor a lithium secondary battery are shown in Tables 3 and 4.

TABLE 3 Sintering Li/Me temperature 0.1 C capa Neutralizer (+additive)(molar ratio) (° C.) K (ppm) (mAh/g) Example 2-1 K₂CO₃ 2[M] (+K₂ CO₃)1.3  900 2000 221 Example 2-2 ↑ ↑ ↑ 4000 236 Example 2-3 ↑ ↑ ↑ 6000 231Example 2-4 ↑ ↑ ↑ 10000 224 Example 2-5 ↑ ↑ ↑ 15000 200 Example 2-6 ↑ ↑↑ 16000 193 Example 2-7 ↑ ↑ ↑ 17000 188 Example 2-8 ↑ ↑ ↑ 18000 180Example 2-9 ↑ ↑ ↑ 1200 203 Example 2-10 ↑ ↑ ↑ 1500 208 Example 2-11 ↑ ↑800 2000 212 Example 2-12 ↑ ↑ ↑ 4000 216 Example 2-13 ↑ ↑ ↑ 6000 218Example 2-14 ↑ ↑ ↑ 10000 215 Example 2-15 ↑ ↑ ↑ 15000 210 Example 2-16 ↑↑ ↑ 16000 195 Example 2-17 ↑ ↑ ↑ 17000 186 Example 2-18 ↑ 1.4  900 2000213 Example 2-19 ↑ ↑ ↑ 4000 215 Example 2-20 ↑ ↑ ↑ 6000 217 Example 2-21↑ ↑ ↑ 10000 214 Example 2-22 ↑ ↑ ↑ 15000 211 Example 2-23 ↑ ↑ ↑ 16000200 Example 2-24 ↑ ↑ ↑ 17000 191 Example 2-25 ↑ ↑ ↑ 18000 183 Example2-26 ↑ ↑ ↑ 1200 191 Example 2-27 ↑ ↑ ↑ 1500 202 Example 2-28 ↑ 1.25 ↑2000 215 Example 2-29 ↑ ↑ ↑ 4000 218 Example 2-30 ↑ ↑ ↑ 6000 218 Example2-31 ↑ ↑ ↑ 10000 216 Example 2-32 ↑ ↑ ↑ 15000 205 Example 2-33 ↑ 1.45 ↑2000 201 Example 2-34 ↑ ↑ ↑ 4000 204 Example 2-35 ↑ ↑ ↑ 6000 210 Example2-36 ↑ ↑ ↑ 10000 207 Example 2-37 ↑ ↑ ↑ 15000 205

TABLE 4 Sintering Li/Me temperature 0.1 C capa Neutralizer (+additive)(molar ratio) (° C.) K (ppm) (mAh/g) Comparative K₂CO₃ 2[M] (+K₂ CO₃)1.3 900 19000 175 Example 2-1 Comparative ↑ ↑ ↑ 20000 170 Example 2-2Comparative ↑ ↑ 800 19000 171 Example 2-3 Comparative ↑ ↑ ↑ 20000 165Example 2-4 Comparative ↑ 1.4 900 19000 179 Example 2-5 Comparative ↑ ↑↑ 20000 173 Example 2-6 Comparative K₂CO₃ 2[M] 1.3 900 1000 165 Example2-7 Comparative K/Li = 1/1[M] ↑ ↑ 600 163 Example 2-8 Comparative K/Li =0.5/1.5[M] ↑ ↑ 300 165 Example 2-9 Comparative Li₂CO₃ 2[M] ↑ ↑ 100 162Example 2-10 Comparative NH₄HCO₃ 2[M] ↑ ↑ 100 156 Example 2-11Comparative K₂CO₃ 2[M] (+ K₂ CO₃) 1.0 900 2000 152 Example 2-12Comparative Li₂CO₃ 2[M] 1.0 ↑ 100 155 Example 2-13

It is apparent from Table 3 that lithium secondary batteries using thepositive active materials of Examples 2-1 to 2-37, in which the Li/Meratio of the lithium transition metal composite oxide is 1.25 to 1.45and K is contained in an amount of 1200 to 18000 ppm, have a highdischarge capacity with the discharge capacity (0.1 C capa) being 180mAh/g or more, and particularly those containing K in an amount of 1500to 15000 ppm have a discharge capacity (0.1 C capa) of 200 mAh/g ormore.

On the other hand, from Table 4, lithium secondary batteries using thepositive active materials in which the Li/Me ratio is 1.25 to 1.45, butthe content of K is less than 1200 ppm for Comparative Examples 2-7 to2-11 and the content of K is more than 18000 ppm for ComparativeExamples 2-1 to 2-6 have a discharge capacity (0.1 C capa) of less than180 mAh/g, and improvement of the discharge capacity is not sufficient.

The lithium secondary battery using a positive active material(LiCo_(1/3)Ni_(1/3)Mn_(1/3)O₂), which is not of so called a“lithium-excess-type” but of so called a “LiMeO₂-type”, has a dischargecapacity (0.1 C capa) of only 152 mAh/g, although the content of K is1200 ppm or more, as shown in Comparative Example 2-12. Moreover, sincethe lithium secondary battery of Comparative Example 2-12 describedabove has a discharge capacity comparable to that of the lithiumsecondary battery of Comparative Example 2-13 using a positive activematerial of the same “LiMeO₂-type” in which the content of K is 100 ppm,such an effect that the discharge capacity is significantly improved byincluding K in a specified amount may be specific to the“lithium-excess-type” positive active material.

In Examples described above, the content of Na, the content of K and thevalue of D50 (D50 particle size) in the particle size distribution ofsecondary particles for the lithium transition metal composite oxide ofthe present invention have been described on the basis of the results ofmaking measurements for the lithium transition metal composite oxide(positive active material) before preparation of the electrode. However,for a lithium secondary battery having history of charge-discharge, thecontent of Na, the content of K and the value of the D50 particle sizecan be determined by carrying out a treatment in accordance with theprocedure described below.

First, a lithium secondary battery having a history of charge-discharge(in the present invention, a lithium secondary battery of which“discharge capacity (mAh/g)” was measured in Example) is sufficientlydischarged by low rate discharge at about 0.1 CmA, and the lithiumsecondary battery is disassembled in an atmosphere with a dew point of−20° C. or lower to take out a positive electrode. The positiveelectrode that is taken out is placed in a thermostatic bath at 80° C.,and dried until an electrolyte solution (solvent) attached thereon issufficiently volatilized. From the positive electrode, a composite (55mg) is taken from a composite layer containing a positive activematerial, and an ICP emission spectroscopic analysis is performedaccording to the procedure described in Example using the obtainedcomposite. The obtained value is converted into a concentration per massof the positive active material.

Using the method described above, the battery was disassembled and theamount of Na contained in the positive electrode was measured aftercharge-discharge for the positive active material of Example 1-5. As aresult, it was found that the content of Na after synthesis of thepositive active material (before the battery was assembled) was 2100ppm, while the content of Na after charge-discharge (after the batterywas disassembled) was 2000 ppm, and thus Na was contained in thepositive electrode in an amount almost equal to the amount of Nacontained in the active material before the battery was assembled.

Using the method described above, the battery was disassembled and theamount of K contained in the positive electrode was measured aftercharge-discharge for the positive active material of Example 2-1. As aresult, it was found that the content of K after synthesis of thepositive active material (before the battery was assembled) was 2000ppm, while the content of K after charge-discharge (after the batterywas disassembled) was also 2000 ppm, and thus K was contained in thepositive electrode in an amount almost equal to the amount of Kcontained in the active material before the battery was assembled.

In a positive electrode using the positive active material of Example, asignificant change was not observed in the contents of Na and K evenafter charge-discharge. Therefore, it can be said that according to themeasurement method described above, the content of Na and/or K in thepositive active material can be measured even for a lithium secondarybattery after charge-discharge.

In a lithium secondary battery using a positive electrode containing thepositive active material of the present invention, Na and/or K in thepositive active material may leak out from the positive electrodedepending on use conditions. In this case, Na and/or K is also containedin an electrolyte solution and a negative electrode, and therefore bymeasuring not only the content of Na and/or K in the positive electrodebut also measuring the amount of Na and/or K contained in theelectrolyte solution and/or the negative electrode, the amount of Naand/or K contained in the positive active material can be known moreaccurately.

By performing a treatment in accordance with the procedure describedbelow for a lithium secondary battery having a history ofcharge-discharge, for which the battery is discharged, the positiveelectrode is taken out and the positive electrode is dried as describedabove, the value of the D50 particle size can be determined.

The positive active material is separated from the positive composite ofthe positive electrode. The positive composite often contains aconducting material and a binder. Examples of the method for removing abinder from the positive composite include a method in which a solventcapable of dissolving the binder is used. For example, when the binderis thought to be polyvinylidene fluoride, mention is made of a method inwhich the positive composite is immersed in a sufficient amount ofN-methylpyrrolidone, heated at 150° C. for several hours, and thenseparated into a powder containing the positive active material and asolvent containing the binder by filtration or the like. For examplewhen the conducting material is thought to be a carbonaceous materialsuch as acetylene black, examples of the method for removing theconducting material from the powder containing the positive activematerial, from which the binder is removed in the manner describedabove, include a method in which the carbonaceous material isoxidatively decomposed to be removed by a heat treatment. Conditions forthe heat treatment are required to include a temperature at which theconducting material is thermally decomposed in an atmosphere includingoxygen, or higher, but if the heat treatment temperature is too high,the properties of the positive active material may be changed, andtherefore such a temperature is desirable that has no influences on theproperties of the positive active material wherever possible. Forexample, in the case of the positive active material of the presentinvention, this temperature may be about 700° C. in the air.

By measuring the positive active material thus obtained for the particlesize in the manner described in paragraph [0095], a value of the D50particle diameter can be determined.

However, in the process of production of the battery and the process ofcharge-discharge of the battery, some positive active material particlesmay be broken. By making a SEM observation of a positive electrode platetaken out from the battery, an approximate ratio at which the positiveactive material is broken can be known. When it can be predicted thatbroken positive active material particles are included, the averageparticle size (D50 particle size) is determined after data is correctedso that particles of 2 μm or less are excluded in a particle sizedistribution curve obtained from measurement for excluding a fine powdergenerated due to breakage.

In the present invention, the discharge capacity may be significantlyimproved by including Na in an amount of 900 ppm or more and 16000 ppmor less or K in an amount of 1200 ppm or more and 18000 ppm or less in apositive active material for a lithium secondary battery which containsa lithium transition metal composite oxide represented by thecomposition formula of Li_(1+α)Me_(1−α)O₂ (Me is a transition metalincluding Co, Ni and Mn and α>0) in view of Examples described above.

By using a positive active material containing a novel lithiumtransition metal composite oxide of the present invention, a lithiumsecondary battery having a high discharge capacity can be provided, andtherefore the lithium secondary battery is useful for hybrid cars andelectric cars.

What is claimed is:
 1. A positive active material for a lithiumsecondary battery, comprising a lithium transition metal composite oxidehaving an α-NaFeO₂-type crystal structure and represented by thecomposition formula of Li_(1+α)Me_(1−α)O₂ (Me is a transition metalincluding Co, Ni and Mn and α>0), wherein the positive active materialcontains Na in an amount of 900 ppm or more and 16000 ppm or less, or Kin an amount of 1200 ppm or more and 18000 ppm or less, a pore size ofthe positive active material which shows a maximum differential porevolume is in a range of 30 to 40 nm, and the positive active materialhas a peak differential pore volume of 0.85 mm³/(g·nm) or more.
 2. Thepositive active material for a lithium secondary battery according toclaim 1, wherein the positive active material has a 50% particle size(D50) of 8 to 10 μm in particle size distribution measurement.
 3. Thepositive active material for a lithium secondary battery according toclaim 1, wherein a molar ratio of Li to Me is represented by (1+α)/(1−α)and is 1.25 to 1.45.
 4. An electrode for a lithium secondary batterycomprising the positive active material for a lithium secondary batteryaccording to claim
 1. 5. A lithium secondary battery comprising theelectrode for a lithium secondary battery according to claim 4.